Vessel for forming a trench in a water bottom

ABSTRACT

A vessel ( 1 ) for forming a trench in a water bottom ( 100 ) includes a ladder ( 2 ) and trenching elements mounted to the ladder ( 2 ). The trenching elements are formed by a first upwardly inclined auger ( 10 ) for forming a first inclined trench wall ( 101 ) and a second upwardly inclined auger ( 20, 20 ′) for forming a second inclined trench wall ( 102 ). The first auger ( 10 ) is arranged to be rotated to move material of the water bottom ( 100 ) in an upward direction along the first auger ( 10 ).

TECHNICAL FIELD

The invention relates to vessel for forming a trench in a water bottom, the vessel comprises a ladder and trenching means mounted to the ladder. The invention further relates to trenching means.

BACKGROUND

Vessels and apparatus for trenching and dredging are known since a long time, such as cutter suction dredgers.

In the magazine Popular Mechanics of April 1956 an article was published with the title “Walking” dredge cuts drainage canal, in which a dredge is described with 4 spuds to brace the dredge during digging. Mounted on its bow is a boom that not only swings up and down, but sidewise as a cutterhead chews away the mud and a suction pipe carries the sludge to the rear of the boom, through a pump and out a discharge pipe at the stern.

Auger type dredging apparatus are known as well. U.S. Pat. No. 5,060,404 describes an auger type dredge head connected to a dredge ladder in one of plurality of angular positions relative to the ladder axis. The auger digger comprises first and second oppositely spiralled digging fins, wherein the auger digger is rotated in a direction wherein said fins propel dredged material in a direction towards the centre. A suction pipe inlet opening is provided in to a region at the centre of the auger differ in a position to receive dredged material propelled theretowards by said oppositely spiralled differ fins.

Vessels arranged to create a trench in the water bottom are known as well. An example of such a vessel is provided by NL1015160C2. The vessel comprises a ladder, on which a cutter head is mounted to create a trench. An alternative is shown in U.S. Pat. No. 2,755,632A.

Trenching may also be done using an apparatus that travels underwater.

U.S. Pat. No. 4,395,158 describes a method and apparatus for entrenching under-water pipelines, in which auger assemblies are provided on a sled or other form of underwater vehicle. The augers are spaced apart and straddle the pipeline, and can pivot to an inwardly inclined position in which the axes of the augers intersect each other at an angle, and the cutting portions of the augers are beneath the pipeline to form a generally V-shaped trench. Alternatives are described in U.S. Pat. No. 3,852,972A and U.S. Pat. No. 4,117,689A.

JP-A-52109291 describes a dredger and not suitable a vessel for forming a trench.

SUMMARY

It is an object to provide a vessel which can form a trench in a water bottom in an improved manner.

According to an aspect there is provided a vessel for forming a trench in a water bottom, the vessel comprises a ladder and trenching means mounted to the ladder, characterized in that the trenching means are formed by a first upwardly inclined auger for forming a first inclined trench wall and a second upwardly inclined auger for forming a second inclined trench wall, wherein the first auger is arranged to be rotated to move material of the water bottom in an upward direction along the first auger.

The term vessel as used here also comprise pontoons, floating docks and the like.

The first and second auger may be driven by driving means (hydraulic) provided on the vessel. The driving means may be connected to the augers via the ladder, for instance by means of a driving shaft or a hydraulic connection. The driving means may be formed by an engine.

The ladder is a construction which is moveable attached to the vessel to position the trenching means on a desired depth with respect to the vessel. The ladder may comprise an elongated frame which is with one end rotatably connected to the vessel to lower and lift the ladder. The trenching means may be provided on or near the opposite end of the frame. The ladder may extend in a forward or rearward direction with respect to the vessel and may be rotatable about an axis substantially horizontal and perpendicular to the forward or rearward direction of the vessel.

An auger is a device which comprises a helical member, for instance a helical blade, which when the auger is rotated functions as a screw conveyor to move material. The helical blade may be provided at the outer circumference of a central member. The central member may widen in a direction into which the material is to be moved. The helical member may also increase in size in the direction into which the material is to be moved. So, in this case, the central member and/or helical member of the first auger may widen/increase in size in the upward direction.

The first and second augers are directed in different inclined directions to form the two side walls of a trench. The upper ends of the first and second augers are thus directed sideways in opposite directions with respect to the longitudinal direction of the trench. As explained below, the first and second augers may also be directed in oblique forward or rearward directions.

The first and second inclined trench walls form the side walls of the trench. The trench may have a substantially V-shaped cross-section. The trench may also be formed by two oppositely inclined trench walls, connected by a substantially horizontal bottom wall.

The first auger is arranged to be rotated to move material of the water bottom in an upward direction, away from the second auger. The first and second auger may be at an angle β, wherein 15°≦β≦60°. Angle β is defined as the angle between the horizontal and a projection of the auger on a vertical plane, the plane being perpendicular to the trenching direction.

By providing two upwardly inclined augers, a trench may be formed in an efficient way, while the disturbance of the surrounding environment is minimal, and no plume or at least only a relatively small plume is created.

According to an embodiment the first and second augers are together orientated in a V-shape.

The first auger forms a first leg of the V-shape and the second auger forms a second leg of the V-shape. The first and second augers may have the same or different lengths. The term V-shape is used here to indicate that the longitudinal body axes of the first and second augers form a V-shape, although the augers itself may not meet or be connected to each other at the tip of the V. Also, the first and second augers may be off-set with respect to each other in a longitudinal direction of the trench which is to be formed. The first and second augers in particular form a V-shape when seen in a trenching direction of the vessel (see FIGS. 1 a and 2 a).

In use, the tip of the V-shape is directed towards the water bottom and in use the first auger is rotated to move material in an upward direction towards the free end of the first auger to move material in an upward and sideways direction to form the trench. The material is deposited at the side of the trench.

The V-shaped augers also provide trenching means which create a relatively low resistance for the vessel, in particular compared to trenching means formed by a plough. The vessel can thus move in a relatively energy-efficient way.

According to an embodiment an upper end of the first upwardly inclined auger is directed in an oblique rearward direction with respect to a trenching direction of the vessel.

The trenching direction of the vessel is the direction in which the vessel moves during formation of the trench.

The vessel may comprise propagation means which define the forward sailing direction of the vessel, of course notwithstanding the fact that the propagation means may also be arranged to steer the vessel in other directions, allowing the vessel to make turns or to sail in a backward direction. The propagation means may also be formed by spuds and respective spud carriages which can move the spuds in a horizontal direction with respect to the vessel to define a trenching direction.

The first upwardly inclined auger is tilted in a backward direction with respect to the trenching direction. The auger may be tilted in a backward direction forming an angle α with respect to the trenching direction, 90°<α<180°, for instance in the range 110°<α<150°. Angle α is defined as the angle between the trenching direction and a projection of the auger on a horizontal plane (see FIGS. 1 b and 2 b).

The longitudinal axis of the first auger may be directed in an oblique rearward direction to take into account the forward motion of the vessel during forming of the trench. As the vessel moves in the trenching direction while material is transported along the auger, the backward tilt ensures that the auger can transport the material along the auger.

According to an embodiment the second auger is arranged to be rotated to move material of the water bottom in an upward direction along the second auger.

By providing two augers which are operated to transport material towards their respect free ends, a trench is created in an efficient manner. The trenching means are formed in a symmetric way, which results in symmetric forces exerted on the ladder and the vessel. Also, as the material is deposited on both sides of the trench, a symmetric trench with symmetric side walls on both sides of the trench is formed.

So, in this case, the central member and/or helical member of the second auger may widen/increase in size in the upward direction. The second auger is arranged to be rotated to move material of the water bottom in an upward direction, away from the first auger. Preferably, the first and second auger are equal in size and configuration.

According to an embodiment an upper end of the second upwardly inclined auger is directed in an oblique rearward direction with respect to a trenching direction of the vessel.

This is done to take into account the forward motion of the vessel during trenching. The first and second augers may be symmetrical with respect to the trench.

The auger may be tilted in a backward direction forming an angle α with respect to the trenching direction, 90°<α<180°, for instance in the range 110°<α<150°. Angle α is defined as the angle between the trenching direction and projection of the auger on a horizontal plane (see FIGS. 1 b and 2 b).

By tilting the augers in a backward direction, the augers can work in an efficient way during forward movement of the vessel.

The orientation of the first and second augers take into account the forward movement of the vessel.

According to an embodiment the second auger is arranged to be rotated to move material of the water bottom in a direction towards the first auger.

In use, the second auger is rotated such that material is moved in a downward direction towards the first auger, where it is picked up by the first auger and moved upwardly towards the free end of the first auger.

The lower end of the second auger is adjacent the lower end of the first auger. The lower end of the second auger may be positioned forward with respect to the lower end of the first auger, with respect to the trailing direction.

According to this embodiment, the material moved to form the trench is deposited on one side of the trench, i.e. on the side of the first auger. This is advantageous in situations where it is desirable to deposit all the material on one particular side of the trench, for instance in shallow water to allow equipment to reach the trench from the other side of the trench where the material is not deposited.

So, in this case, the central member and/or helical member of the second auger may widen/increase in size in the downward direction.

According to an embodiment the second auger has a smaller moving capacity than the first auger.

The first auger is preferably larger, i.e. has a larger moving capacity, than the second auger, as the first auger not only moves material released from the water bottom by the first auger, but also the material received from the second auger. The second auger may therefore have a smaller helical member, for instance a smaller helical blade, or a central member having a smaller diameter.

According to an embodiment an upper end of the second upwardly inclined auger is directed in an oblique forward direction with respect to a trenching direction of the vessel.

The second auger may be directed in a forward direction to take into account the movement of the vessel during trenching. The second auger may be tilted in a forward direction forming an angle α′ with respect to the trenching direction, 0°<α′<90°, for instance in the range 20°-60°. Angle α′ is defined as the angle between the trenching direction and projection of the auger on a horizontal plane. The first and second auger may be in line with each other when seen from above, i.e. α+α′=180° (see FIG. 2 b).

According to an embodiment the trenching means are provided at a bow of the vessel.

According to such an embodiment, in use, the trenching means are pushed by the vessel. This turned out to be particularly advantageous for embodiments with first and second upwardly inclined augers directed in an oblique rearward direction.

According to an embodiment the trenching means are provided at a stern of the vessel.

According to such an embodiment, in use, the trenching means are pulled by the vessel. This turned out to be particularly advantageous for embodiments with asymmetric trenching means, such as trenching means with a first upwardly inclined auger directed in an oblique rearward direction and a second upwardly inclined auger directed in an oblique forward direction.

According to an embodiment the trenching means comprise a plough, positioned behind the first and second auger. The ploughs are positioned direct behind the augers to detain the soil, making sure its picked up by the augers. The term behind is to be understood as relative to the trenching direction.

According to an embodiment the vessel comprises a plurality of spuds and respective spud carriages which can move the spuds in a horizontal direction with respect to the vessel to define a trenching direction.

A spud is a pile that is used by vessels and which can engage with the water bottom in order to provide a fixed point for such a vessel. The spud, also referred to as spud-pile, has a substantial vertical orientation and is subjected to loads, in particular resulting from the trenching process and wind, current and waves influencing the vessel. In practice, a spud weighs between a few dozen tons and 200 tons. The spud may be made of steel and may comprise drain holes and holes for receiving locking pins.

The spud may be lowered to engage with the water bottom. This may be done by simply releasing the spud such that it falls to the water bottom. The lower end of the spud may be formed as a sharp end to penetrate the water bottom. Lifting means are provided for lifting the spud.

One or more spud guiders may be provided connected to the vessel for accommodating the spud and guiding the spud when it is lowered or lifted. In order to provide the vessel freedom of movement with respect to the spud, the spud guiders may be provided on a spud carriage which can move relative to the hull of the vessel in a predefined horizontal direction. This allows to move the vessel in a predefined direction during trenching, thereby defining the trenching direction. The use of spuds makes the vessel less vulnerable to wind, waves and currents and allows to control the velocity of the vessel in an accurate manner.

The vessel may comprise four spuds, which are in pairs applied alternatingly, to move the vessel in the trenching direction.

According to an embodiment the ladder is moveably mounted to lift and lower the trenching means. The ladder may thus be moved to adjust the depth of the trenching means and thus adjust the depth of the trench which is to be formed.

According to an embodiment the vessel comprises adjustment means, for adjusting the orientation and/or relative position of the first and second augers.

The adjustment means may be formed by cranes positioned on the deck of the vessel, each crane comprising a hoisting cable connected to one of the first or second auger. By adjusting the length of the hoisting cable and/or adjust the orientation of the crane, the orientation of the first and second auger may be adjusted. The first and second augers are rotatable connected to the ladder.

The adjustment means may also be formed by hydraulic cylinders, provided between the augers and the vessel or the ladder for positioning the augers. The adjustment means may also be formed by a rotation mechanism provided in or near the rotatable connection of the first and second augers with the ladder.

Adjusting the orientation and/or relative position of the first and second augers may be done to adjust the trenching means to the type of soil, the depth of the trench which is to be formed, the width of the trench which is to be formed, the speed of the vessel etc.

For instance, angle β as discussed above may be adjusted to adjust the steepness of the trench walls.

Also, angle α (and α′) as discussed above may be adjusted to adjust the orientation of the first and second auger to the speed of the vessel. Angle α may be chosen larger (and α′ smaller) when the speed of the vessel during trenching is higher.

The adjustment means may also be arranged to adjust the distance between the first and second augers, for instance in a direction perpendicular to the trenching direction and/or in a direction parallel to the trenching direction.

According to a further aspect there is provided a method of trenching comprising

-   -   providing a vessel with a ladder and trenching means mounted to         the ladder,     -   lowering the ladder to position the trenching means at a         predetermined depth,

characterized by the trenching means being formed by a first upwardly inclined auger for forming a first inclined trench wall and a second upwardly inclined auger for forming a second inclined trench wall, the method further comprising

-   -   rotating the first auger to move material of the water bottom in         an upward direction along the first auger while moving the         vessel in a trenching direction.

The method may further comprise rotating the second auger to move material of the water bottom in an upward direction along the second auger while moving the vessel in a trenching direction.

Alternatively the method may further comprise rotating the second auger to move material of the water bottom in an downward direction along the second auger towards the first auger while moving the vessel in a trenching direction.

According to an embodiment the method further comprising adjusting the orientation and/or relative position of the first and second augers.

This is done before starting forming of the trench. Optionally, the orientation and/or relative position of the first and second auger may be adjusted during trenching to take into account changing circumstances, such as changes of the type of soil, the depth of the trench which is to be formed, the width of the trench which is to be formed, the speed of the vessel etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

FIGS. 1 a-c schematically show an embodiment in a front view, top view and side view respectively, and

FIGS. 2 a-c schematically show an alternative embodiment in a front view, top view and side view respectively.

The figures are meant for illustrative purposes only, and shall not serve as restriction of the scope or the protection as laid down by the claims.

DETAILED DESCRIPTION

With reference to the figures, embodiments will now be described in more detail.

FIGS. 1 a-1 c show a vessel according to an embodiment.

The vessel 1 comprises a ladder 2 to which trenching means are mounted. The vessel comprises a bow 3 and a stern 4. The ladder may be provided at the bow 3 or at the stern 4.

The ladder 2 may be arranged to move the trenching means up and down to adjust the relative position of the trenching means with respect to the vessel 1. This is shown in FIG. 1 c, in which the ladder 2 and thus the trenching means are shown in three different positions.

The vessel 1 is arranged to move in a trenching direction T (see FIG. 1 b).

FIG. 1 a shows two augers 10, 20 which are positioned in an upwardly inclined orientation, the first auger 10 and the second auger 20 being directed in opposite side directions with respect to the trenching direction. The first and second auger 10, 20 are substantially positioned in a V-shape orientation, although the first and second augers 10, 20 may be off-set with respect to each other in the trenching direction and/or in a horizontal direction perpendicular to the trenching direction.

The first and second augers 10, 20 are tilted upwardly at an angle β, as indicated in FIG. 1 a. An upper end (11) of the first upwardly inclined auger 10 and an upper end 21 of the second upwardly inclined auger 20 are directed in opposite oblique rearward directions with respect to the trenching direction T of the vessel 1. The first auger 10 is thus positioned to form a first inclined trench wall 101 and the second auger is positioned to form a second inclined trench wall 102, opposite the first inclined trench wall 101.

Optionally, as shown in the FIGS. 1 a-1 c, the first and second inclined augers 10, 20 are directed in opposite oblique rearward directions with respect to the trenching direction T of the vessel 1. This is best shown in FIG. 1 b, showing a top view of the vessel 1. In FIG. 1 b angles α are indicated.

Both the first and second augers 10, 20 are arranged to be operated to move material from the water bottom 100 in an upward direction along the respective first and second augers 10, 20. This way, a trench is formed as shown in FIG. 1 a, with banks on both sides of the trench.

The first and second augers 10, 20 are further suspended by cranes 40 and hoisting cables 41 (shown in FIG. 1 c).

The cranes 40 with hoisting cables 41 may be provided to support the augers 10, 20 and may also function as adjustment means to adjust he orientation and or relative position of the augers 10, 20. The cranes 40 and hoisting cables 41 may be used as adjustment means to adjust the relative position of the first and second augers 10, 20. The position of the top of the cranes 40 may be adjusted by moving the cranes 40. Also, the free length of the hoisting cables 41 may be varied to lift or lower the upper ends of the augers 10, 20. Winching means (not shown) may be provided to vary the length of the hoisting cables 41. This way, angles α and β may be adjusted. Also, the off-set of the first and second augers may be adjusted, in a direction perpendicular to the trenching direction T, as well as in a direction parallel to the trenching direction T.

It will be understood that further or alternative adjustment means may be provided, such as hydraulic actuators provided between the augers and the vessel 1 or ladder 2.

The first and second augers 10, 20 may be rotatably connected to the ladder 2, for instance by a universal joint or the like, that is capable of transmitting rotary motion to rotate the augers 10, 20 and allow the first and second augers to assume different relative orientations with respect to the ladder 2.

A plough 120 may be provided, preferably directly behind the first and second augers 10, 20 with respect to the trenching direction T. The plough 120 may comprise two ploughing walls 121 which have lower edges which help to define the shape of the trench to be formed.

The ploughing walls 121 may meet in the middle forming a substantially vertical ploughing edge 122 to cut through the water bottom 100 and move material of the water bottom 100 towards the first and second augers 10, 20. The plough 120 is an optional feature.

The vessel 1 is arranged to move in a trenching direction T. The vessel may therefore comprise propagating means, in the embodiments shown formed by a plurality of spuds 30 and spud carriages 31. In the embodiments shown, four spuds 30 are provided. Two spuds 30 may be lowered to engage the water bottom 100. The spud carriages 31 are then moved in a horizontal direction to move the vessel 1 with respect to the lowered spuds 30, thereby moving the vessel 1. Once the carriages 31 can't be moved any further, the other two spuds 30 may be lowered to engage the water bottom 100 and the first two spuds 30 are lifted. This way the vessel 1 may be moved in a accurate and controlled manner.

FIGS. 2 a-2 c show an alternative embodiment. As shown in FIGS. 2 a -2 c, the second auger 20′ is directed in an opposite oblique direction compared to the first auger 10 with respect to the trenching direction T. When seen from above, the first and second auger are in line (see FIG. 2 b).

The upper end 21′ of the second upwardly inclined auger 20′ is directed in an oblique forward direction with respect to a trenching direction T of the vessel 1.

It is noted that in use the vessel 1 according to FIGS. 2 a-c moves in the opposite direction compared to the vessel shown in FIGS. 1 a-c. The second auger 20′ can be operated to transport material of the water bottom in a direction towards the first auger 10, where it is picked up by the first auger 10 which transports the material in an upward direction along the first auger 10. This way a trench is formed with a bank on one side.

As the first auger 10 will have to transport more material than the second auger 20′, the moving capacity of the first auger may be larger than the second auger 20′,

Operation of the Embodiments

Next, the operation of the vessel 1 will be described. Before starting forming a trench, the ladder 2 to which the trenching means are mounted is lowered to a predetermined depth. Also, the orientation and mutual position of the first and second augers 10, 20 is set using the adjustment means described above.

Once the first and second augers 10, 20 are positioned, the vessel may be moved in the trenching means using the propagating means described above, such as the spuds 30 and spud carriages 31 described above. At the same time, the first and second augers 10, 20 are driven to rotate to move material from the water bottom. The first auger 10 may be driven to move material of the water bottom (100) in an upward direction along the first auger 10. The second auger 20 may be driven to move material of the water bottom 100 in an upward direction along the second auger 20 (embodiments described with reference to FIGS. 1 a-1 c) or in a downward direction along the second auger 20′ towards the first auger 10 (embodiments described with reference to FIGS. 2 a-2 c).

During trenching, the orientation and/or relative position of the first and second augers 10, 20 may be adjusted to take into account changing conditions.

Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention. 

1-16. (canceled)
 17. A vessel for forming a trench in a water bottom, comprises a ladder and trenching means mounted to the ladder, wherein the trenching means are formed by a first upwardly inclined auger for forming a first inclined trench wall and a second upwardly inclined auger for forming a second inclined trench wall, wherein the first auger is arranged to be rotated to move material of the water bottom in an upward direction along the first auger.
 18. The vessel according to claim 17, wherein the first and second augers are together orientated in a V-shape.
 19. The vessel according to claim 17, wherein an upper end of the first upwardly inclined auger is directed in an oblique rearward direction with respect to a trenching direction of the vessel.
 20. The vessel according to claim 17, wherein the second auger is arranged to be rotated to move material off the water bottom in an upward direction along the second auger.
 21. The vessel according to claim 20, wherein an upper end of the second upwardly inclined auger is directed in an oblique rearward direction with respect to a trenching direction of the vessel.
 22. The vessel according to claim 17, wherein the second auger is arranged to be rotated to move material of the water bottom in a direction towards the first auger.
 23. The vessel according to claim 22, wherein the second auger has a smaller moving capacity than the first auger.
 24. The vessel according to claim 20, wherein an upper end of the second upwardly inclined auger is directed in an oblique forward direction with respect to a trenching direction of the vessel.
 25. The vessel according to claim 17, wherein the trenching means are provided at a bow of the vessel.
 26. The vessel according to claim 17, wherein the trenching means are provided at a stern of the vessel.
 27. The vessel according to claim 17, wherein the trenching means comprise a plough, positioned behind the first and second auger.
 28. The vessel according to claim 17, wherein the vessel comprises a plurality of spuds and respective spud carriages which can move the spuds in a horizontal direction with respect to the vessel to define a trenching direction.
 29. The vessel according to claim 17, wherein the ladder is moveably mounted to lift and lower the trenching means.
 30. The vessel according to claim 17, wherein the vessel comprises adjustment means, for adjusting the orientation and/or relative position of the first and second augers.
 31. A method of trenching comprising providing a vessel with a ladder and trenching means mounted to the ladder, lowering the ladder to position the trenching means at a predetermined depth, wherein the trenching means are formed by a first upwardly inclined auger for forming a first inclined trench wall and a second upwardly inclined auger for forming a second inclined trench wall, the method further comprising rotating the first auger to move material of the water bottom in an upward direction along the first auger while moving the vessel in a trenching direction.
 32. The method according to claim 31, further comprising adjusting the orientation and/or relative position of the first and second augers. 